This invention relates to identification apparatus based upon biometrics and, in particular, to a photodetector having an integral EL lamp in which the rear electrode of the lamp is the fingertip of a person.
It has been a continuing problem to provide unique, secure means for identifying individuals, whether for security in a manufacturing plant or for identifying a party to an electronic business transaction. Thefts of a person""s xe2x80x9cidentityxe2x80x9d have been increasing as thieves become more sophisticated in exploiting modern technology. The unique physiological features of an individual, e.g. retina, fingerprint, voice, and auricle, have long been used for identification. The problem remains of providing an electronic identification system that exploits such unique features to provide a rapid, secure identification system.
It is known in the art to use an EL lamp for illuminating a fingerprint; U.S. Pat. No. 5,781,651 (Hsiao et al.). It is also known in the art that one can produce a luminous image of a fingerprint by omitting the rear electrode from an EL lamp and having a person touch the rear of the lamp to complete a circuit through the lamp. The current is very small and is not harmful. A series of bright lines are produced by the EL lamp, corresponding to the ridges of the person""s fingerprint. Creating a durable lamp for this purpose has proven elusive, as has providing a suitable detector for converting the luminous image into data for a computer.
An EL lamp is essentially a capacitor having a dielectric layer between two conductive electrodes, one of which is transparent. The dielectric layer includes a phosphor powder or there is a separate layer of phosphor powder adjacent the dielectric layer. The phosphor powder radiates light in the presence of a strong electric field, using very little current.
A modern EL lamp is a thick film device, typically including a transparent substrate of polyester or polycarbonate material having a thickness of about 7.0 mils (0.178 mm.). A transparent, front electrode of indium tin oxide (ITO) or indium oxide is vacuum deposited onto the substrate to a thickness of 1000 xc3x85 or so. A phosphor layer is screen printed over the front electrode and a dielectric layer is screen printed over phosphor layer. A rear electrode, if present, is screen printed over the dielectric layer.
The light from a phosphor particle is radiated essentially in all directions, which is normally an advantage because an EL lamp is a diffuse, uniform light source. The spreading of the light causes problem with contrast and sharpness in a fine line image such as a fingerprint.
It is known to use an optical system to project the luminous image of a fingerprint onto a photodetector but an optical system considerably increases the cost of a fingerprint detector. One can electronically manipulate the image of a fingerprint to try to improve sharpness and contrast but such circuitry or software also increases the cost of a fingerprint detector. Even if a photodetector, such as a charge coupled device, were placed directly against an EL lamp, the light would spread sufficiently for the lines forming the fingerprint to be larger than the area of skin actually in contact with the lamp.
It is known in the art to make an EL lamp by laminating layers together. U.S. Pat. No. 4,560,902 (Kardon) discloses depositing a dielectric film on a sheet of aluminum foil, depositing a phosphor layer on a Mylar(copyright) sheet coated with indium tin oxide, and then laminating the two sheets together.
U.S. Pat. No. 5,469,109 (Mori) discloses laminating two coated, transparent sheets together wherein a first sheet includes a transparent electrode, a phosphor layer, and a dielectric layer and a second sheet includes an adhesive layer and a rear electrode overlying the adhesive layer. The adhesive layer is larger than the rear electrode and contacts the first sheet, enclosing the phosphor layer and the dielectric layer to seal the lamp.
In view of the foregoing, it is therefore an object of the invention to provide an EL lamp that creates a luminous image that faithfully represents a fine line image.
Another object of the invention is to provide biometric apparatus including an EL lamp closely coupled optically to a photodetector.
A further object of the invention is to improve image sharpness and contrast in a fingerprint detector including an EL lamp.
Another object of the invention is to provide a method for reliably making an EL lamp on a semiconductor substrate.
The foregoing objects are achieved by the invention in which lamp materials, e.g. a phosphor layer and a dielectric layer, are roll coated onto a release layer. A photodetector is coated with a translucent conductive layer and the lamp materials are laminated to the transparent conductive layer. The release layer is removed and a protective coating is applied to the dielectric layer. A resin coating is optionally applied to the transparent conductive layer prior to lamination to improve adhesion. The protective coating can be incorporated into the lamp materials prior to lamination. The release layer can be coated by screen printing or other deposition technique.